Application of a kinetic model to predict extracted ion profiles for the identification of evaporated ignitable liquids

Abstract

A kinetic model was previously developed in our laboratory to predict evaporation rate constants of compounds in ignitable liquids as a function of gas chromatographic retention index. The model is applied to the chromatogram of an unevaporated liquid and used to predict chromatograms corresponding to any evaporation level of the liquid. In previous work, accuracy in predicting total ion chromatograms (TICs) for gasoline and petroleum distillates was demonstrated. In this work, the model is applied for the first time to predict extracted ion profiles (EIPs) corresponding to different compound classes.Fifteen ignitable liquids representing five classes (isoparaffinic, naphthenic-paraffinic, aromatic, petroleum distillate, and gasoline) defined in ASTM E1618 were experimentally evaporated to 50–90% (v/v). The kinetic model was applied to predict TICs and EIPs corresponding to the alkane, cycloalkane, aromatic, indane, and polynuclear aromatic compound classes for each evaporated liquid. Strong correlation between experimental and predicted TICs and EIPs indicated the predictive accuracy of the model. Reference collections were then generated containing predicted TICs and EIPs for each liquid corresponding to evaporation levels ranging from 10 to 90%. The reference collections were used to identify the ignitable liquid class in samples of increasing complexity, based on maximum correlation between the experimental and predicted chromatograms. In all cases, the correct liquid class was identified, even in the presence of substrate interferences. Overall, this work demonstrates the potential of a kinetic model to generate TICs and EIPs as a practical tool for identification of ignitable liquids in fire debris samples.